A recording/reproducing apparatus is a device that performs data processing for recording or reproducing data on or from a recording medium such as an optical disc including a compact disc (CD) or a digital versatile disc (DVD). It is necessary for the recording/reproducing apparatus to perform tracking control so as to perform data processing for recording or reproducing data on or from the recording medium while following its track.
Such conventional tracking control uses a 1-beam push-pull method. The 1-beam push-pull tracking control will now be described in detail with reference to FIG. 1. A laser beam reflected from a recording medium is incident on an optical detector 300 through an objective lens 200. The optical detector 300, which is divided into two areas A and B, converts the laser beam received through the areas A and B into electrical signals and outputs them as signals A and B. A difference signal between the signals A and B is used as a tracking error signal (TE). When the laser beam is located at the center of the track, the magnitude of the tracking error signal is minimized (i.e., TE=0). Therefore, tracking control is performed by moving the objective lens 2 left and right horizontally with respect to the recording medium so that the magnitude of the tracking error signal (TE) is minimized (i.e., TE=0). This makes it possible to control the laser beam to follow the track without leaving the track.
However, the conventional method has the following problems.
In the 1-beam push-pull method, when the objective lens is moved horizontally left and right, a laser beam incident on the optical detector is also moved horizontally left and right, thereby causing an optical offset between the areas A and B. Since the optical offset is not separated from a signal change caused by a tracking error, the optical offset causes an error in tracking control for an eccentric recording medium.
In addition, since the optical offset is not separated from a signal change caused by leaving the track when performing real-time tracking control, the optical offset causes an error in tracking control for an eccentric recording medium.
Further, the optical offset varies depending on the intensity of light reflected from the recording medium. It is difficult to cancel the optical offset of a recording medium such as a rewritable recording medium which includes both a non-recorded area having a high reflectance and a recorded area having a low reflectance.